pidgin, libmaxminddb, simutrans, tiptop: remove myself

... from meta.maintainers. I haven't been willing to spend
nontrivial effort on these packages in the past year or more.
I don't use them anymore.

pkgs/applications/networking/instant-messengers/pidgin/default.nix

···
     homepage = "https://pidgin.im/";
     license = licenses.gpl2Plus;
     platforms = platforms.unix;
-    maintainers = [ maintainers.vcunat ];
+    maintainers = [ ];
   };
 };
 

pkgs/development/libraries/libmaxminddb/default.nix

···
     description = "C library for working with MaxMind geolocation DB files";
     homepage = "https://github.com/maxmind/libmaxminddb";
     license = licenses.asl20;
-    maintainers = [ maintainers.vcunat ];
+    maintainers = [ ];
     mainProgram = "mmdblookup";
     platforms = platforms.all;
   };

pkgs/games/simutrans/default.nix

···
 
       homepage = "http://www.simutrans.com/";
       license = with licenses; [ artistic1 gpl1Plus ];
-      maintainers = with maintainers; [ vcunat phile314 ];
+      maintainers = with maintainers; [ phile314 ];
       platforms = with platforms; linux; # TODO: ++ darwin;
     };
   };

pkgs/os-specific/linux/tiptop/default.nix

···
     homepage = "http://tiptop.gforge.inria.fr";
     license = licenses.gpl2;
     platforms = platforms.linux;
-    maintainers = [ maintainers.vcunat ];
+    maintainers = [ ];
   };
 }